And plz don't say wankism. That's similar thing, but not so popular. So what's a better way to express?
The word, which notoriously is an instance of the phenomenon, is
the practice of using very long words. Also sesquipedalism, sesquipedality. — sesquipedal, sesquipedalian, adj. (Free Dictionary)
These people would be pedantic
1. ostentatious in one's learning.
2. overly concerned with minute details or formalisms, esp. in teaching. http://www.thefreedictionary.com/pedantic
@BrianDonovan and @Baiwir have answered this question with the assumption that the speaker is using the long words correctly, even though their meaning may be obscure to the speaker's companions. My own word choice, in this case, would be obscurantism(2): "a style... characterized by deliberate vagueness or abstruseness".
However, it's not clear to me that that's what the OP meant by the question; I was instead reminded of Mr. Ballou, a character from Mark Twain's humorous memoir Roughing It:
What Mr. Ballou customarily meant, when he used a long word, was a secret between himself and his Maker... His one striking peculiarity was his Partingtonian fashion of loving and using big words for their own sakes, and independent of any bearing they might have upon the thought he was purposing to convey. He always let his ponderous syllables fall with an easy unconsciousness that left them wholly without offensiveness. In truth his air was so natural and so simple that one was always catching himself accepting his stately sentences as meaning something, when they really meant nothing in the world. If a word was long and grand and resonant, that was sufficient to win the old man's love, and he would drop that word into the most out-of-the-way place in a sentence or a subject, and be as pleased with it as if it were perfectly luminous with meaning.
Based on this passage, I propose "Partingtonian". As far as I can tell, Twain was referring to an 1873 book called Partingtonian Patchwork by B.P. Shillaber, which is full of humorous examples of long words misused and misunderstood. (The Partington family are among the chief characters in the book, hence "Partingtonian".)
As the term "Partingtonian" is no longer in common use (although Twain's original readers must have recognized it), it has the advantage that you, too, will be using a word that nobody else will understand!
On the other hand, since Mark Twain is still widely read while Shillaber has faded from memory, perhaps "Ballouvian" might be an acceptable alternative?